The Caves of Nanumanga are a complex of submerged sea caves on the reef off the northern tip of the island. In 1986 two New Zealand divers found a hidden chamber inside, with blackened walls and what they identified as fire pits or hearths. If the interpretation is correct, the caves were dry, above-sea-level shelters used by people thousands of years before Polynesians are thought to have reached Tuvalu.
The site sparked decades of academic debate and has never been fully excavated. Access is difficult — the entrance is about 40 metres deep and the local council does not encourage casual visits. Most travellers see only the surface markers; the caves themselves are reserved for serious divers with permission from the island council.